Optical parallel transmission device

ABSTRACT

A parallel optical transmission device is disclosed, which comprises a transmitter section having one or a plurality of transmitter modules converting one or a plurality of input electric signals into optical signals; a section consisting of bundles of optical waveguides 20i, j transmitting the optical signals; and a receiver section having one or a plurality of receiver modules reproducing the electric signals from the optical signals thus transmitted to output them; wherein all propagation delay times from the input electric signals to the output electric signals are set in predetermined regions.

This is a continuation of application Ser. No. 08/049,714 filed Apr. 20,1993 now U.S. Pat. No. 5,448,661.

BACKGROUND OF THE INVENTION

The present invention relates to an optical transmission device and inparticular to a parallel synchronous transmission device using a bundleof optical waveguides such as an optical fiber array, etc. and atransmission system using same.

Signal transmission techniques with a high speed and a high density arerequired in a computer or an exchange and transmission system. It ispredicted that in electric signal transmission using coaxial cables ortransmission paths utilized heretofore there is a limit in the speed andthe density due to crosstalk, electric power consumption in transmissioncircuits, etc. On the contrary, an optical waveguide has in general awide pass band and a low crosstalk. Further it is a light and fine line.In addition, there are no problems due to a grounding potentialdifference.

As described in Reference 1) K. Kaeda et al., "Twelve-channel paralleloptical fiber transmission using a low drive-current 1.3 μm LED arrayand a PIN PD array", Technical Digest of 1989 Optical FiberCommunication Conference, TUD3 and Reference 2) Y. Ota and R. G. Swartz,"Multi-channel Optical Data LINK (MODLINK)" Third OptoelectronicsConference (OEC'90) Technical Digest, 11D1-5, a plurality of signals areoptically transmitted in parallel by means of an optical element arrayand an optical waveguide array which contrasts with to prior arttransmission by means of one optical waveguide (optical fiber).

As described in the two references cited above, one of the most seriousproblems in a parallel transmission device consists in skew within anarray. Reference 1) states that skew in a 12-channel 1 km multimodefiber (GI62.5) array is 8 ns. On the other hand, Reference 2) describesthat skew within an array in a 12-channel multimode fiber (62.5/125GI)ribbon is 10 ns/km and that in practice skew compensation is necessary.In FIG. 1 of Reference 2), an optical deskewer is connected after antransmitter (Tx).

These prior art examples discuss skew within an array in a paralleltransmission device (link array) using one fiber array or a fiberribbon. According thereto, the number of channels in parallel in thearray should be increased in order to increase the number of channels inparallel of signals. However there is a limit in the number of channelsin parallel due to a limit in production.

Reference 2) deals with the possibility of extension. Since this systemis characterized in skew regulation of an optical fiber for everychannel, it is possible to increase the number of channels thereof byeffecting skew regulation for all the channels. However, by this method,since the skew regulation is effected for every combination of fibersand transmitting-receiving modules, there are problems in productivity,maintenance, etc.

Conventionally,.for example, Japanese patent publication JP-A 64-48011discloses a parallel data transmission optical cable which performsparallel transmission of data at high speed between computers andbetween computer terminals using a plurality of optical fibers.

SUMMARY OF THE INVENTION

The present invention provides means for realizing multi-channelparallel synchronous transmission, which is excellent in massproductivity, ease of maintenance, economic property and exchangeabilityand which can be standardized.

In order to achieve this, signal propagation time is controlled. Theskew represents relative time differences between different signalpropagation times and absolute time of the signal propagation time forevery array is controlled for securing simultaneous arrival of signalsfor different arrays. The number of channels in parallel can beincreased without regulation by arranging in parallel a number oftransmitting-receiving modules, for which this absolute time of thesignal propagation time is controlled.

In order to realize this control, the respective signal propagationtimes from an electric signal input to an optical output reference plane(or optical connector contact plane) in a transmitter section (ormodule) and from an optical input reference plane (or optical connectorcontact plane) to an electric signal output in a receiver section (ormodule) and the signal propagation time for each of bundles of opticalwaveguides such as fiber arrays, etc. are regulated so as to be inregions predetermined for them, respectively. In this way it is possibleto standardize different parts and to realize a high productivity, aneasy maintenance, a good economic property and a high exchangeability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 indicates the operation of the present invention.

FIG. 2 shows the construction of a first embodiment of the presentinvention.

FIG. 3 shows the construction of a transmitter module to be used in theembodiment of FIG. 2.

FIG. 4 is a perspective view of a laser array submount to be used in thetransmitter of FIG. 3.

FIG. 5 is a block diagram of a transmitting IC circuit.

FIG. 6 shows the construction of a receiver module to be used in theembodiment of FIG. 2.

FIG. 7 is a perspective view of a photodiode array submount to be usedin the receiver of FIG. 6.

FIG. 8 is a block diagram of a receiving IC circuit.

FIG. 9 shows a system for measuring the propagation delay time in afiber array cable.

FIG. 10 shows a system for measuring the propagation delay time in afiber array cable, using a reference fiber.

FIG. 11 shows the construction of a second embodiment of the presentinvention.

FIG. 12 shows the construction of a transmitter-receiver module to beused in the embodiment of FIG. 11.

FIG. 13 shows the construction of a third embodiment of the presentinvention.

FIG. 14 shows the construction of a transmitter-receiver module for usein the embodiment of FIG. 13.

FIG. 15 shows the construction of a plug-in type transmitter submodule.

FIG. 16 shows the construction of a plug-in type receiver submodule522"9.

FIG. 17 is an equivalent circuit diagram of a receiving IC.

DETAILED DESCRIPTION

FIG. 1 indicates the principle of the present invention. An opticalparallel transmission device according to the present invention iscomposed of transmitter modules 1j (j=1˜N) having multi-channelconnectors 401, j (j=1˜N), receiver modules 3j (j=1˜N) havingmulti-channel connectors 40K, j (j=1˜N) and bundles of opticalwaveguides 20i, j (i=2˜K, j=1˜N) connected therewith throughmulti-channel connectors 40i, j (i=2˜K, j=1˜N).

Electric signals inputted to the transmitter modules 1j (j=1˜N) areconverted into optical signals propagated to the receiver modules 3j(j=1˜N), where corresponding output electric signals are reproduced. Atthis time, signals inputted through pins 10j (j=1˜N) can be transmittedsynchronously to pins 30j (j=1˜N) owing to the fact that the absolutevalue of propagation time from the input pins 10j (j=1˜N) for the inputelectric signals to the output pins 30j (j=1˜N) for the output electricsignals is set in a predetermined region.

At this time, the signal propagation times from the input pins 10j(j=1˜N) to the multi-channel connectors 401, j (j=1˜N), from themulti-channel connectors 40i, j (i=2˜K, j=1˜N) to 40K, j (j=1˜N) andfrom the multi-channel connectors 40K, j (j=1˜N) to the output pins 30j(j=1˜N) are set in predetermined regions, respectively. In this way,parts can be standardized and it is possible to realize an easymaintenance, a good economic property and a high exchangeability.

FIG. 1 indicates only the basic construction and in practice variousvariations are conceivable for the construction of the bundles ofoptical waveguides. In particular cables consisting of different numbersof optical waveguides may be used between different multi-channelconnectors. For example, it can be thought that between themulti-channel connectors 401, j (j=1˜N) and 402, j (j=1˜N) n waveguides,n being the number of channels in each transmitter module, are bundledin one cable and between the multi-channel connectors 402, j (j=1˜N) and403, j (j=1˜N) nN waveguides are bundled in one cable so that they areconnected apparently through one cable. Further, when the transmitter orreceiver modules are of plug-in type, the propagation time between theend plane of the optical waveguides in each module and the input oroutput electric signal pins may be within a predetermined region.

Further, although data transmission in one direction is indicated inFIG. 1, a bidirectional structure is also conceivable.

As described above, various structures are conceivable and for all ofthem it is possible to intend to standardize parts and to effectsynchronous transmission with a great number of channels in parallel bysetting the signal propagation time for every part in a predeterminedregion.

Hereinbelow the first embodiment will be explained, referring to FIGS. 2to 10.

FIG. 2 shows the construction thereof. Transmitter modules 1a and 1b andreceiver modules 3a and 3b for optical parallel transmission withpigtail fiber arrays are mounted on boards 100A and 100B, respectively,on which logic circuits within a logic device are mounted, which modulesare connected through fiber array cables 20a and 20b, respectively.

8-bit data of an IC 63a on the board 100A and clocks from a clockdistributing IC 60 are transmitted synchronously in parallel to an IC62a and a clock distributing IC 61 on the board 100B through thetransmitter module 1a, a fiber array 20a including 9 fibers and areceiver module 3a. Similarly 8-bit data of an IC 63b on the board 100 Aare transmitted synchronously in parallel to an IC 62b on the board 100Bthrough the transmitter module 1b, a fiber array 20b and a receivermodule 3b. In the present embodiment, a reference clock is generated onthe board 100 A and it is distributed to the board 100B.

Hereinbelow a hardware construction will be indicated.

The transmitter and receiver modules 1a, 1b, 3a and 3b include pigtailfiber arrays 12a, 12b, 32a and 32b, respectively, each of which has amulti-channel optical connector at one end thereof. The multi-channeloptical connector is fixed by an edge of a board. This edge was appliedto the back panel side and to a front panel, which is opposite thereto.When the multi-channel optical connector was fixed to the edge on theback panel side, a plug-in type multi-channel connector was mounted onthe back panel.

FIGS. 3 and 6 indicate the construction of the transmitter and thereceiver module used in the present embodiment respectively; FIGS. 4 and7 represent a laser array and a photodiode array, respectively, mountedon a submount; and FIGS. 5 and 8 are block diagrams indicating atransmitting and a receiving IC circuit, respectively. In FIGS. 3 and 6a part of the pigtail fiber array and the multi-channel opticalconnectors are omitted.

The transmitter module indicated in FIG. 3 consists of 9 electric signalinputs and 2 pins for power supply 10; an IC substrate 16, on which alaser array driving IC 13 is mounted; a laser array 15 secured to asubmount 19; a 9-channel pigtail fiber array 12; a first metal block18a, to which the IC substrate 16 and the laser array submount 19 aresecured by soldering; a piece of silicon 17a having V-shaped grooves forfixing fibers of the pigtail fiber array 12 at predetermined positionsand a piece of silicon 17b for pressing down the fibers and fixing themby soldering; and a second metal block 18b, on which the piece ofsilicon 17a is fixed by soldering, and a metal package 11 accommodatingthese parts. Electric signals inputted through the pins 10 drive thelaser array in the IC 13 to be converted into optical signals, which aresent to the fiber array.

Optical coupling between the laser array 15 and the fiber array 12 iseffected by holding the first and the second metal block 18a and 18b insuch a positional relationship that coupling between the two ends of thearrays is maximum in a state where the lasers are excited so as to emitlight and by securing them to the metal package 11 by soldering. At theoptical coupling, provisional wire bonding on the wiring for lightemission disposed on the IC substrate 16 is effected so as to excite.the lasers at the two ends to emit light and the wiring is removedafter the termination of the fixation of the optical coupling bysoldering described above.

The part of the package, through which the pins 10 and the fiber array12 were taken out, was constructed so as to be airtight, using solder.Further reliability of the module was increased owing to the fact thatsolder used in the package was fluxless.

The length of the pigtail fiber array was measured before the opticalcoupling and the multi-channel optical connector was formed at one endthereof. In the present embodiment the length of the fiber array is 26.0cm; fluctuations in the length due to errors in the length measurement,abrasion of the fibers at the formation of the multi-channel opticalconnector, etc. are smaller than 3 mm; and the propagation time of theoptical signals is shorter than 15 ps. Further the skew within the fiberarray is smaller than about 1 ps.

The laser array is formed on a p conductivity type semiconductorsubstrate and this p conductivity type semiconductor substrate serves asa p side common terminal for all the lasers. The lasers are mounted on asubmount and control of characteristics thereof, etc. are effected. FIG.4 indicates the laser array mounted on the submount. The laser array 15is secured by soldering to the metal block 190, to which a wiring board191 is soldered and every laser electrode is wirebonded with the wiringboard. Since the metal package 11 is designed so as to be at the groundpotential, the p side common terminal of the lasers is connected withthe metal package 11 with low parasitic elements through the submountmetal block 190 and the first metal block 18a to be grounded. In thisway it was possible to reduce electric crosstalk in the laser array.

Each of the lasers has a multiple quantum well active layer structure; ashort cavity of 150 μm; and a highly reflective end surface of 70%-90%.The interval between lasers is 250 μm and the threshold current issmaller than 3 mA.

FIG. 5 indicates the IC circuit. It was fabricated by using Si bipolarIC process. It is composed of a driving circuit section consisting ofelectric inputs INi (i=1˜9); current outputs Iouti (i=1˜9); inputbuffers IBi (i=1˜9); constant current generating transistors Q3i(i=1˜9); and a pair of transistors Q1i (i=1˜9) and Q2i (i=1˜9) switchingconstant currents thus generated, and a circuit 161 generating necessarycontrol voltages. Since the threshold current was small, the no biasdriving method was adopted. Modulation current was 20 mA. For the layoutof the IC the driving circuits were arranged with the same interval asthe lasers. In this way it was possible to reduce fluctuations in thedelay time within the IC.

In the present embodiment using the construction described above thesignal propagation time from the electric signal input pins 10 to theinput end of the pigtail fiber was 0.2 ns±70 ps and the signalpropagation time of the pigtail fiber was 1.3 ns±15 ps. The signalpropagation time from the electric signal input pins 10 to the end ofthe multi-channel optical connector is 1.5 ns±85 ps. However, since thelasers are driven without bias, a light emission delay of at most 500 psis produced at the rise.

The receiver module indicated in FIG. 6 consists of a 9-channel pigtailfiber array 32; a photodiode array 35 secured to a submount 39; an ICsubstrate 36, on which a receiver IC 33 is mounted; 9 electric signaloutputs and 2 pins for power supply 30; a first metal block 38a, towhich the IC substrate 36 and the photodiode array submount 39 aresecured by soldering; a piece of silicon 37a having V-shaped grooves forfixing fibers of the pigtail fiber array 32 at predetermined positionsand a piece of silicon 37b for pressing down the fiber cores and fixingthem by soldering; and a second metal block 38b, on which the piece ofsilicon 37a is fixed by soldering, and a metal package 31 accommodatingthese parts. The electric signals are reproduced from the opticalsignals from the fiber array 32 by the photodiodes and the receiving ICand outputted through the pins 30.

Optical coupling between the photodiode array 35 and the fiber array 32is effected by holding the first and the second metal block 38a and 38bin such a positional relationship that coupling between the two ends ofthe arrays is maximum in a state where light is inputted from the fibersat the two extremities of the fiber array and by securing them to themetal package 31 by soldering. At the optical coupling, provisional wirebonding on the wiring for light reception disposed on the IC substrate36 is effected so as to monitor photocurrents of the photodiodes at thetwo extremities and the wiring is removed after the termination of thefixation of the optical coupling by soldering described above.

Similar to the transmitter module, the part of the package, throughwhich the pins 30 and the fiber array 32 were taken out, was constructedso as to be airtight, using solder. Further reliability of the modulewas increased owing to the fact that solder used in the package wasfluxless.

Similar to the transmitter module, the length of the pigtail fiber arraywas measured before the optical coupling and the multi-channel opticalconnector was formed at one end thereof. In the present embodiment thelength of the fiber array is 26.8 cm; fluctuations in the propagationtime of the optical signals are smaller than 15 ps. Further the skewwithin the fiber array is smaller than about 1 ps.

The photodiode array is formed on an n conductivity type semiconductorsubstrate and this n conductivity type semiconductor substrate serves asan n side common terminal for all the photodiodes. In order to reducethe capacity, a rear injection type was adopted. The photodiodes aremounted on a submount and control of characteristics thereof, etc. areeffected. FIG. 7 indicates the photodiode array mounted on the submount.Three surfaces 391, 392 and 393 of a ceramic block 390 are metallizedand patterned and the photodiodes are diebonded on the surface 392. Thesurface 393 is used for wiring the wire-bonding with the IC substrate 36and the surface 391 is used for grounding pattern. It was possible toreduce electric crosstalk produced on the ground side of the photodiodesowing to the fact that the photodiode array was grounded to the metalpackage 31 with low parasitic elements through the first metal block38a, using the grounding pattern.

FIG. 8 indicates the IC circuit. Similar to the transmitter module, itwas fabricated by using Si bipolar IC process. It is composed of achannel receiving circuit section consisting of photocurrent inputterminals Iini (i=1˜9); signal outputs Vouti (i=1˜9); preamplifyingcircuits PREi (i=1˜9); post amplifiers POSTi (i=1˜9); COMPi (i=1˜9)having discriminating function; and output buffers OBi (i=1˜9), and acircuit 361 generating necessary control voltages. For the layout of theIC the circuits were arranged with the same interval as the photodiodes.In this way it was possible to reduce fluctuations in the delay time(skew) within the IC. However, in this receiving circuit, since theamplification factor is not regulated, depending on inputted lightpower, increase or decrease in the amplitude due to variations in thedecision point at rise/fall is produced.

In the present embodiment using the construction described above thesignal propagation time from the pigtail output end to the electricsignal output pins 30 was 1.2 ns±135 ps and the signal propagation timeof the pigtail fiber was 1.3 ns±15 ps. The signal propagation time fromthe multi-channel optical connector to the electric signal output pins30 was 2.5 ns±150 ps. However, since a fixed amplification/fixeddecision point method is used, the pulse width increases or decreaseswithin a region of a half of rise/fall time, depending on light inputpower.

The two boards are connected through a fiber array cable havingmulti-channel optical connectors at the two ends. In the presentembodiment single mode fibers were used for all the fiber arraysincluding the pigtail. The propagation delay time of a fiber array cablewas around 500 ns and fluctuations thereof were 400 ps.

A method for fabricating a cable, whose propagation delay time iscontrolled with a high precision, will be explained. At first, a fiberarray cable longer than that determined by a required propagation timeis cut out from a cable, using a length measuring apparatus. In thepresent embodiment the cable thus cut out is 101 m long. The precisionof the length measuring apparatus is about 50 cm for this extent oflength. Therefore the propagation delay of the fiber array is in aregion from 5002.5 to 5007.5 ns. A multi-channel optical connector isconnected at one end of this fiber array cable. In the presentembodiment the length of the fiber array cable lost thereby is shorterthan 1 mm, which corresponds to a propagation time shorter than 0.005ns.

FIG. 9 shows a system for measuring the propagation delay time of fiberarray cables, which system is composed of a high precision oscillator200; an extremely short light pulse generator 210 synchronized with theoscillator 200; an optical isolator 211; a light waveform measuringdevice 220; an optical bidirectional coupler 230; multi-channel opticalconnector--one channel optical connector converting jigs 240 and 241.Errors in the fiber length from the optical bidirectional coupler 230 tothe multi-channel optical connector of each of the converting jigs 240and 241 are smaller than 1 cm. Light pulses generated by the extremelyshort light pulse generator 210 are 40 ps wide. The fiber array cable20, at one end of which the multi-channel optical connector isconnected, described previously is connected with the converting jig 240and the propagation time thereof is measured.

Measurement is effected by observing an arrival time difference of areflected light pulse through fibers to be measured in the fiber arraycable 20 by means of the light waveform measuring device 220. Repeatedpulses are generated by the high precision oscillator 200 with a timeinterval, which is twice as long as the desired propagation time, or atime interval as short as the desired propagation time divided by aninteger and light pulses p0 thus generated are inputted to the opticalbidirectional coupler 230. The light pulses p0 are separated into lightpulses p1 and p2 having almost identical light intensities by theoptical bidirectional coupler 230. Respective reflected pulses r1 and r2of the light pulses p1 and p2 are unified and superposition of thereflected lights r1 and r2 is observed. The arrival time difference ofthe reflected light r1 is observed by means of the light waveformmeasuring device 220, using the reflected light r2 as the reference, onehalf thereof being the propagation delay time of one fiber in the fiberarray cable 20. Calibration is effected by carrying out measurements ina state without fiber array cable.

On the other hand, FIG. 10 shows a system for measuring the propagationdelay time of a fiber array cable, using a reference fiber. Measurementis effected by the same principle as that explained, referring to FIG.9, i.e., the arrival time difference of reflected light pulses from thereference fiber 201 and one fiber in the fiber array cable 20 isobserved by means of the light waveform measuring device 220.Calibration is effected by carrying out measurements in a state withoutreference fiber 201 nor fiber array cable 20. The propagation delay timeof the reference fiber 201 is measured by means of the system indicatedin FIG. 9.

While measuring the propagation time by means of either the systemindicated in FIG. 9 or FIG. 10, the cables are cut so that all thepropagation times thereof are in a predetermined region, taking thefiber array length lost at the connection of the multi-channel opticalconnector into account. In the present embodiment the propagation delaytime of one fiber in the fiber array cable is measured and errors in thepropagation time are converted in the length with a rate of 5 ns/m.Errors were set at first below 500 ps (below 10 cm in the length) and atthe second time they were set below 25 ps (below 0.5 cm in the length).At this time, since fluctuations of the propagation time among differentfibers in a single mode fiber array are smaller than 3 ps/m,fluctuations in the propagation time among the different fibers in thecable are smaller than 300 ps, because the length of the cable in thepresent embodiment is about 100 m. Thereafter a multi-channel opticalconnector is connected at the open end of the cable. The propagationtime of the fibers satisfies the specification (500 ns±400 ps), takingabrasion of the fibers at the mounting of the connector and measurementerrors of 40 ps into account.

The apparent electric signal propagation time of the paralleltransmission system using the transmitter-receiver modules and the fiberarray cable is 504 ns±640 ps. In practice, the final specification onthe fluctuations of the light propagation time is determined, takingfluctuations of the light propagation time due to wiring shape of thefiber array cable into account.

Since the signal propagation time of electric signals can be controlledwith a high precision as described above, the two boards 100A and 100Bcan exchange data synchronously. Further synchronism can be kept, evenif a plurality of such parallel transmission systems are wired in orderto increase the amount of transmitted data.

However delay of rise due to delay in the laser light emission andincrease or decrease in the pulse width due to jitter and rise/fall timein the receiving circuit should be taken into account. System designtaking them into account is possible. Countermeasures against the delayin the laser light emission can be taken by latching it at a fall, forwhich no delay in the light emission takes place. Increase or decreasein the pulse width due to rise/fall time may be considered as wiringskew.

In order to reduce any increase or decrease in the pulse width due torise/fall time, countermeasures can be taken by adding a circuit, whichvaries the amplification factor, depending on inputted light power andkeeps the pulse width at the discrimination constant. However sincethese measures complicate the receiving circuit and increase electricpower consumption, they are used only for signals specifically requiringthem.

Although Si bipolar ICs are used in the above description, other kindsof ICs may be used, taking exchangeability with other logic circuitsinto account. Further, even if the kind of ICs and electric signalinterfaces differ for the transmission and the reception, no problemstake place, if the delay time by the ICs is controlled.

In addition, although a p conductivity type substrate is used for thelaser array, an n conductivity type substrate may be used. Various sortsof structures may be conceivable. Further, although the no bias drivingmethod is adopted for the sake of simplicity in the present embodiment,it is possible also to apply a bias voltage to ICs. Still further LEDsmay be used. A p conductivity type substrate may be used also for thephotodiode array. A front injection type may be also adopted.

Although single mode fibers are used, multimode fibers may be also usedfor distances as short as about 20 m. Further a combination, by whichmultimode is used only for the pigtail fiber in the receiver module,etc. is conceivable.

Hereinbelow a second embodiment of the present invention will beexplained, referring to FIGS. 11 and 12.

FIG. 11 shows the construction thereof. Transmitter and receiver modules5A1˜5 and 5B1˜5 for parallel optical transmission are mounted on boards101A and 101B in logic devices 800A and 800 B, respectively, andconnected through two kinds of fiber array cables 20A1˜5, 22 and 20B1˜5.The transmitter and receiver modules 5A1˜5 and 5B1˜5 are constructed soas to have transmitting 16 channels and receiving 16 channels, i.e., 32channels in all. Different devices are connected bidirectionally through80 channels. Each of the fiber array cables 20A1˜5 has 32 channels,which are composed of four 8-channel fiber arrays, and the fiber arraycable 22 has 160 channels, which are constructed by bundling twenty8-channel fiber arrays. Each of the fiber array cables 20A1˜5 and 20B1˜5has two 32-channel optical connectors at the extremities. The fiberarray cable 22 has two 160-channel optical connectors, each of which iscomposed of five 32-channel optical connectors, at the extremities. Thelight output section of each of the transmitter and receiver modules5A1˜5 and 5B1˜5 consists of a 32-channel optical connector and the32-channel optical connector at one end of each of the fiber arraycables 20A1˜5 is connected directly with a transmitter - receiver modulepackage. The 32-channel optical connector at the other end of each ofthe fiber array cables 20A1˜5 is connected with the 160-channel fiberarray cable 22 through an optical connector adapter 440A mounted on thecasing of the device 800A. The fiber array cable 22 is connected withthe fiber array cables 20B1˜5 through an optical connector 440B mountedon the casing of the device 800B.

Clocks for the devices 800A and 800B are supplied from clockgenerating - distributing sections 810A and 810B, respectively. Datasignals transmitted - received and sent in parallel from clockdistributing ICs 60A and 60B by transmitter - receiver modules 5A3 and5B3 are synchronized with device clocks through elastic buffer ICs 62A,63A and 62B, 63B, respectively.

FIG. 12 shows the construction of the transmitter - receiver modules5A1˜5 and 5B1˜5. Each of the transmitter - receiver modules 5A1˜5 and5B1˜5 is composed of two 8-channel transmitter submodules 510 and 511and two 8-channel receiver submodules 520 and 521. The transmitter andthe receiver modules have the same structure as the transmitter and thereceiver modules indicated in FIGS. 3 and 6, respectively, although theyare different in the number of channels. However the pigtail fiberarrays are as short as 36 mm and they are accommodated in packages.Further the different pigtail fiber arrays are connected with ferrules541, 542, 543 and 544, respectively.

Each of the present transmitter - receiver modules 5 is constructed bysecuring the pigtail fiber array transmitter submodules 510 and 511 andthe receiver submodules 520 and 521 assembled independently from eachother with ferrules to the transmitter - receiver module package 530acting also as a heat sink. Thereafter the 32-channel optical connectoris assembled. Each of the ferrules 541, 542, 543 and 544 has two guidepins. (For example, the ferrule 544 has guide pin holes 550 and 551.)The 32-channel optical connector is secured to a ferrule case 450 sothat these ferrules have a certain degree of freedom. For example, theferrule 541 is fixed by two nails 581 (one of them being not seen in thefigure) disposed on the upper and the lower side of the ferruleinsertion hole therefor in the ferrule case 450.

Further each of the submodules has four positioning pins for the purposeof securing it to the transmitter - receiver module package 530 with ahigh precision and for effecting positioning of the electric pins with ahigh precision at mounting the boards. (For example, the submodule 521has pins 561, 562, 563 and 564.) Holes, in which the pins are inserted,are formed in the transmitter - receiver module package 530 with aprecision of 0.05 mm. (For example, holes 571 and 572 are formed in thesubmodule 521.) Further holes, in which the pins are inserted, areformed in the board with a precision of 0.1 mm.

The pigtail fiber arrays are 36 mm long both for the transmission andfor the reception. Errors in the length measurement and fluctuations dueto abrasion of fiber at the formation of the multi-channel opticalconnector are smaller than 3 mm and fluctuations in the optical signalpropagation time are smaller than 15 ps. Further skew within an fiberarray is smaller than about 1 ps.

In the present embodiment using the construction described above thesignal propagation time from the electric signal input pins 10 to thepigtail input end was 0.2 ns±70 ps and the signal propagation time ofthe pigtail fiber was 0.18 ns±15 ps. The signal propagation time fromthe electric signal input pins 10 to the end of the multi-channeloptical connector was 0.38 ns±85 ps. However, since the lasers aredriven without bias, a light emission delay of at most 500 ps isproduced at the rise.

In the present embodiment using the construction described above thesignal propagation time from the pigtail output end to the electricsignal output pins 30 was 1.2 ns±135 ps and the signal propagation timeof the pigtail fiber was 0.18 ns±15 ps. The signal propagation time fromthe multi-channel optical connector to the electric signal output pins30 was 1.38 ns±150 ps. However, since a fixed amplification/fixeddiscrimination point method is used, the pulse width increases-ordecreases within a region of a half of rise/fall time, depending onlight input power.

The boards are connected through two kinds of fiber array cables. Eachof the fiber array cables 20A1˜5 and 20B1˜5 has 32 channels, which arecomposed of four 8-channel fiber arrays, and the fiber array cable 22has 160 channels, which are constructed by bundling twenty 8-channelfiber arrays. Also in the present embodiment, single mode fibers areused for all the fiber arrays including the pigtails. The propagationdelay times of the 32-channel and the 160-channel fiber array cable arein predetermined regions. The skew in the 32-channel fiber array cableis 3 ps/m similar to Embodiment 1. However the skew in the 160-channelfiber array cable is 8 ps/m due to the shape effect of bundled fibers.In the present embodiment a specification was so decided that thepropagation delay times of the 32-channel and the 160-channel fiberarray cable are in regions of 10.0 ns±6 ps (about 2 m) and 500 ns±800 ps(about 100 m), respectively.

The propagation delay time in this system was 521.8 ns±2.0 ns. In thepresent embodiment, since clocks are transmitted together with signalsand synchronization is realized by means of elastic buffers on thereceiver side, the propagation delay time and the clocks may beindependent.

By the 32-channel fiber cable array information transmission as effectedin two opposite directions, using two 8-channel fiber arrays (or 16fibers) for each direction. By the 160-channel fiber cable arrayinformation transmission is effected in two opposite directions, usingten 8-channel fiber arrays (or 80 fibers) for each direction.

According to the present embodiment parallel synchronous transmissioncan be effected bidirectionally by using one fiber array cable betweentwo devices.

Hereinbelow a third embodiment of the present invention will beexplained, referring to FIGS. 13 to 17.

FIG. 13 shows the construction thereof. Transmitter and receiver modules5C1˜16 and 5D1˜16 for parallel optical transmission are mounted onboards 102A and 102B in a logic device 804 and connected through fiberarray cables 24-1˜16. The transmitter and receiver modules 5C1˜16 and5D1˜16 are constructed so as to have transmitting 64 channels andreceiving 64 channels, i.e. 128 channels in all. Different devices areconnected bidirectionally mutually through 2048 channels. Each of thefiber array cables 24-1˜16 has 128 channels, which are constructed bybundling sixteen 8-channel fiber arrays. The transmitter - receivermodules 5C1˜16 and 5D1˜16 are connected directly with a 128-channeloptical connector at one end of each of the fiber array cables 24-1˜16.

Clocks for the device 804 are supplied from a clock generating anddistributing section 110. Clocks and synchronizing signals aredistributed from the clock generating and distributing section 110 toboards 102A and 102B through cables having a same length so that the twoboards 102A and 102B are driven synchronously. Distribution of theclocks and synchronizing signals was effected by using the transmitter -receiver module described in Embodiment 1. That is, they are distributedfrom the clock generating and distributing section 110 to the boards102A and 102B through receiver modules 5E1 and 5E2 by transmittermodules 5F1 and 5F2.

The signal propagation time from the input pins to the output pins ofthe transmitter - receiver module is an integer times as long as theclock period. In the present embodiment the signal propagation time fromthe input pins to the output pins of the transmitter - receiver modulewas 12 ns, which corresponds to three clock periods of 4 ns. Thereception output is latched by the clock for the boards within thetransmitter - receiver module.

FIG. 14 indicates the construction of the transmitter - receiver modules5C1˜16 and 5D1˜16 used in the present embodiment. Each of thetransmitter - receiver modules is composed of 8 plug-in type transmittersubmodules 512˜9 and 8 plug-in type receiver submodules 522˜9. These 16submodules are fixed by a case 490 effecting also heat evacuation (onlya part thereof being indicated in the figure). Each of the submoduleshas a positioning pin (pin 565 in the submodule 522) and a holecorresponding thereto (not seen in the figure). The submodule is securedin one body by the case together therewith.

FIG. 15 indicates the construction of the plug-in type transmittersubmodules 512˜19. The transmitter submodule consists of 8 electricsignal inputs and 3 pins for power supply 10; an IC substrate 16, onwhich a laser array driving IC 13 is mounted; a laser array 15 securedto a submount 19; a metal block 18a, to which the IC substrate 16 andthe laser array submount 19 are secured by soldering; a microlens array570 for airtightness and optical coupling; and ferrule positioning pins552 and 553. For the laser arrays 15 and the laser array driving IC 13those used in Embodiment 1 were used, whereby the number of channels was8.

FIG. 16 indicates the construction of the plug-in type receiversubmodules 522˜9. The receiver submodule consists of 8 electric signaloutputs and 3 pins for power supply 30; an IC substrate 36, on which alaser array driving IC 33 is mounted; a photodiode array 35 secured to asubmount 39; a metal block 38a, to which the IC substrate 36 and thesubmount 39 are secured by soldering; a microlens array 570 forairtightness and optical coupling; and ferrule positioning pins 556 and557. The photodiode arrays 35 were those used in Embodiment 1, in whichthe number of channels was 8. FIG. 17 indicates an equivalent circuitdiagram of the receiving IC 33. Although it is identical to that used inEmbodiment 1, data latches FF1˜8, a clock input CLK and a clock bufferCKLB are added thereto. Received data are latched by clocks on theboards as described previously.

The transmitter submodules 512˜19 and the receiver submodules 522˜9 areof so-called plug-in type and optical coupling between the laser array15 or the photodiode array 15 and the fiber arrays is realized directlyby inserting the ferrule 545 into the package of the submodule, asindicated in FIGS. 15 and 16. At this time, optical axis adjustment iseffected by means of pins 552, 553, 556 and 557 for positioning thesubmodule as well as ferrule guide pins 554 and 555.

In the transmitter - receiver module used in the present embodiment, theICs are perpendicular to the plane, on which the boards 102A and 102Bare mounted. This is because, if they were parallel thereto, theinterval between the submodules would be determined by the chip size,which gives rise to a limit in downsizing.

In the present embodiment the fiber arrays were of multi-mode type and2.24 m long. The propagation delay times in the transmitter module, thereceiver module from the optical input to the latch, including the skewdepending on light input, and the fiber array are 0.2 ns±70 ps, 0.6ns±575 ps and 11.4 ns±40 ps, respectively, and it is 12.2 ns±685 ps inall. In this way it was possible to realize a relatively small skew withrespect to the clock period of 4 ns.

Also in the present embodiment, single mode fiber arrays may be usedsimilarly to the other embodiments. Further the latch in the receiversubmodule can be omitted, if it is unnecessary (the ICs in Embodiment 1being used), and it is possible also to use it properly, depending onthe kind of signals. Still further it is possible also to dispose alatch for input signals in the transmitter module or to use properly amodule with latch or without latch, depending on the kind of signals.

In addition, it is possible also to have a margin by setting a wholepropagation delay time by taking into account (subtracting) a fixeddelay on a board (for example a delay time from the closest logicsection to the transmitter - receiver module) from a period an integertimes as long as a clock period.

An extremely great number of synchronous transmissions in parallel canbe effected by using a parallel optical transmission device according tothe present invention, in which the propagation delay time from theinput electric signal to the output electric signal is set in apredetermined region. In this way, it is possible to realize a highspeed and high density wiring by making efficient use of lightness andfineness of a fiber.

Further it is possible to realize an extremely great number ofsynchronous transmissions in parallel, which are suitable forstandardizing parts and excellent in mass productivity, easiness ofmaintenance and economic property, by utilizing a method, by which thepropagation delay time in different constituent elements is controlled,in order to realize the above object.

Furthermore connecting work can be simplified and laying work is madeeasier by bundling fiber bundles, for which the propagation delay timeis controlled for every bundle.

In addition, synchronized boards or devices can be connected withoutdata synchronization by relating the clock period to the propagationdelay time. Still further the present invention can be used also fordistributing clocks or synchronizing signals for synchronizing boards ordevices.

The devices according to the present invention can be mounted with ahigh density by making transmitters, receivers or both in one body byusing positioning pins, etc. Mounting density can be increased furtherby devising the mounting of ICs.

What is claimed is:
 1. A parallel optical transmission devicecomprising:a transmitter section having a plurality of transmittermodules converting a plurality of input electrical signals into opticalsignals; a section consisting of bundles of optical waveguides 20i, jtransmitting said optical signals, one end of said bundles beingconnected with said transmitter section; and a receiver section having aplurality of receiver modules reproducing the electrical signals fromsaid optical signals thus transmitted to output them, said receiversection being connected with the other end of said bundles; wherein allpropagation delay times from said input electrical signals to the outputelectrical signals are set in predetermined regions.
 2. A paralleloptical transmission device comprising:a transmitter section having aplurality of transmitter modules converting a plurality of inputelectrical signals into optical signals; a section consisting of bundlesof optical waveguides 20i, j transmitting said optical signals; and areceiver section having a plurality of receiver modules reproducing theelectrical signals from said optical signals thus transmitted to outputthem; wherein all propagation delay times from said input electricalsignals to the output electrical signals are set in predeterminedregions, and said plurality of transmitter modules and bundles ofoptical waveguides connected directly with said transmitter modules areformed in one body.
 3. A parallel optical transmission devicecomprising:a transmitter section having a plurality of transmittermodules converting a plurality of input electrical signals into opticalsignals; a section consisting of bundles of optical waveguides 20i, jtransmitting said optical signals; and a receiver section having aplurality of receiver modules reproducing the electrical signals fromsaid optical signals thus transmitted to output them; wherein allpropagation delay times from said input electrical signals to the outputelectrical signals are set in predetermined regions, and said pluralityof receiver modules and bundles of optical waveguides connected directlywith said receiver modules are formed in one body.
 4. A parallel opticaltransmission device comprising:a transmitter section having a pluralityof transmitter modules converting a plurality of input electricalsignals into optical signals; a section consisting of bundles of opticalwaveguides 20i, j transmitting said optical signals; and a receiversection having a plurality of receiver modules reproducing theelectrical signals from said optical signals thus transmitted to outputthem; wherein all propagation delay times from said input electricalsignals to the output electrical signals are set in predeterminedregions, and said plurality of transmitter modules, bundles of opticalwaveguides connected directly with said transmitter modules, and saidreceiver modules connected with said bundles of optical waveguides areformed in one body.
 5. A parallel optical transmission devicecomprising:a transmitter section having a plurality of transmittermodules converting a plurality of input electrical signals into opticalsignals; a plurality of bundles of optical waveguides transmitting saidoptical signals, one end of said bundles being connected with saidtransmitter section; and a receiver section having a plurality ofreceiver modules reproducing the electrical signals from said opticalsignals thus transmitted to output them, said receiver section beingconnected with the other end of said bundles; wherein the differencebetween optical signals propagation times of the respective bundles isset in predetermined regions.
 6. A parallel optical transmission devicecomprising:a transmitter section having one transmitter moduleconverting input electrical signals into optical signals; a sectionconsisting of bundles of optical waveguides 20i, j transmitting saidoptical signals, one end of said bundles being connected with saidtransmitter section; and a receiver section having one receiver modulereproducing the electrical signals from said optical signals thustransmitted to output them, said receiver section being connected withthe other end of said bundles; wherein all propagation delay times fromsaid input electrical signals to the output electrical signals are setin predetermined regions.
 7. A bi-directional parallel opticaltransmission device, comprising:a plurality of firsttransmitter-receiver modules each module including a transmitter moduleconverting a plurality of input electrical signals into optical signalsand a receiver module reproducing second electrical signals from otheroptical signals; and a plurality of second transmitter-receiver moduleseach including a second transmitted module converting a plurality ofsaid second input electrical signals into said other optical signals anda second receiver module reproducing said plurality of input electricalsignals from said optical signals coupling said plurality of first andsecond transmitter-receiver modules, wherein all propagation delay timesof input electrical signals are set in predetermined regions.